Generic snap-action switches, also known as “jump” switches, are switches where the switching positions are formed by reversible geometry changes of their movable switching contacts. When switching these snap-action switches the switching positions are converted into electrical signals. A snap-action switch is characterized in that, at a certain position of an actuating structure, it automatically and abruptly generates a change in switching state. Of all switch types, snap-action switches are closest to the mathematically ideal snap-action function of a switch.
The behavior of switches with sliding contacts is regularly dependent on the movement of an actuation structure over a dead path. While in the dead path of the actuating structure both the opening and the closing circuits are open so that the actuating structure may have a negative influence upon the switchover time. Snap-action switches do not suffer from this disadvantage. With snap-action switches the movable switching contact has a constant switchover time known as snap-action time, in which both the opening and the closing circuits are open. The service life of switches with sliding contacts is substantially limited by abrasions occurring on the sliding contacts. In the course of this service life the electric characteristic values deteriorate as a result of this wear from abrasion, in particular the resistance of the switch deteriorates depending on the number of actuating and temperature cycles of switching operations carried out. In order to reduce this wear on the sliding contacts, it is known to lubricate these with lubricants. At low temperatures, when the viscosity of the lubricant is reduced, the electric characteristic values deteriorate, in particular electric resistances rise and the switchover times of switches lengthen.
Snap-action switches are regularly used as signal switches for low direct currents, where bounce time is an important functional criterion. The bounce time is an indication for the time duration which a switching contact, after starting the snap-action operation, requires until an electrical signal is stable. Apart from the actual bouncing operation, recording also encompasses other parameters such as surface effects, including breaking through covering layers at the switching contacts, pushing lubricant out of the contact region and abrading corrosion products on the switching contacts. Due to these surface effects switches with sliding contacts comprise a bounce time which, in particular at low temperatures, is greater than the bounce time of snap-action switches. In order to improve electric conductivity between the switching contacts, their contact surfaces are normally coated galvanically with gold or silver. Gold is used, in particular, on contact surfaces which require a maximum of corrosion resistance. The use of precious metals however makes manufacture of the switches very expensive.
German patent specification DE 10 2006 043 795 B3 and the associated U.S. Pat. No. 8,053,693 B2 both disclose an electric micro switch the switching contacts of which comprise a special surface structure for reducing the bounce time and its contact surfaces are selectively electroplated for minimizing precious metal consumption. For a large-scale production of these switches the contact surfaces are normally electroplated using a punch strip. This technique known as continuous electroplating represents a highly productive and cost-efficient manufacturing method which is suitable in particular for selective coatings and smallest coating thicknesses. However continuous electroplating is a highly specialized and capital-intensive manufacturing process which requires setting up an external supply chain. Such supply chains are however disadvantageous when aiming at vertical manufacturing depth, small batch sizes, low stocks and flexibility in changing process variables.
Known snap-action switches comprise a plurality of components. The German patent specification DE 10 2008 035 043 B4 has disclosed a snap-action switch which is built into a carrier component and is electrically connected with a circuit by soldering, welding or clamping. In order to protect the junctions against moisture and other environmental influences, these are encapsulated in a housing. The junctions however remain a cause for functional failure.
In principle all snap-action switches with metallic contacts and all sliding switches generate switching noises. In many areas however, the demand is now for low-noise or nearly noiseless switches because noises arising from switch actuation are perceived as increasingly annoying. As an example we would mention vehicles with an automatic start-stop system or electrical vehicles where switching noises are audible which are reliably masked in vehicles with conventional combustion engines.
Rating of switches is effected with respect to their weight, their use of energy, their material consumption as well as the number of manufacturing steps required. Advantages compared to classical solutions with carrier components, punched circuit carriers or circuit boards, seals and plugs are offered by a constructive integration of individual switch functions into the flexible circuit carrier.
The German laid-open specification DE 10 2012 005 964 A1 and the German patent application with reference no. 10 2012 007 075.6 both describe switch arrangements, where connection contacting of the switching contacts with the conductor tracks is omitted. In these switch arrangements the flexible circuit carriers assume the function of the switching contacts thereby eliminating the risk of failure originating from the junctions. Even encapsulating the junctions with a plastic may be waived because the flexible circuit carrier is normally provided with a protective coating. In all, because functions are redistributed in these switch arrangements, material consumption is reduced, as is the weight.
The German laid-open specification DE 10 2007 049 692 A1 has disclosed a snap-action switch which is soldered onto a circuit board by means of SMD technology. With this design the number of components, albeit, is reduced, but it comprises soldering points which are susceptible to failure. A further embodiment of a snap-action switch acting as a push-button switch is known from the U.S. Pat. No. 8,129,643 B2, where the basic element is a snap disc, but the number of components could not be reduced.